Alternating-current generator



W. S. MOODY. ALTERNATING CURRENT GENERATOR.

(No Model.)

No. 560,735. Patented May 26, 1896.

ITNSSES UNITED STATES PATENT OFFICE.

TVALTER S. MOODY, OF LYNN, MASSACHUSETTS, ASSIGNOR TO THE GENERALELECTRIC COMPANY, OF NETV YORK.

ALTERNATlNG-CURRENT GENERATOR.

SPECIFICATION forming part of Letters Patent No. 560,735, dated May 26,1896.

I Application filed January 17, 1896- Serial No. 575,828. (No model.)

To all whom, it may concern.- as to compound or overcompound properly,Be it known that I, \VALTER S. MOODY, a the excitation coming on tooslowly when the citizen of the United States, residingat Lynn, currentfalls and falling off too slowly when in the county of Essex, State ofMassachuthe load drops. Another objection to the 5 5 setts, haveinvented certain new and useful use of the single exciter is that withalter- Improvements in Regulating Alternatingnators having largearmature selfinduction Current Dynamo Electric Machines, (Oase (which istrue of the majority of those in use) No. 323,) of which the followingis a specitithe field-current is very much larger at low cation. loadthan at no load, so that in case of a IO My invention relates to theregulation of alsmall amount of overcompounding, such asternating-current dynamo-electric machines, ten per cent. or so, theremay be one hundred and more particularly to the compounding of per cent.or even one hundred and fifty per such machines for change of potentialupon cent. increase in the field-current. A single change of load. Theobjects thus pointed compound-wound eXciter furnishing, say, one I 5 outhave been attained to a greater or less hundred and ten volts whenfullload is on the perfection by other forms of apparatus; butalternating-machine at a light load or no load some of these deviceshave been objectionmust run at a potential of about fifty volts able forvarious reasons. One principal or less. W'ith this condition of weakfield in method in use has been to use a separate exthe exciter thecurrent in its field-magnet 2o citer for such machines and to commute awinding will be extremely unstable and may part of the current of themain machine and fall below the critical point, so that the mapass itaround the field-magnets of the exchine will lose its excitationentirely. This citer, so that the potential of the eXciting-curfact hasbeen practically demonstrated within rent rises with the increase ofload, and thus my knowledge in large machines in commermore current ispassed around the field-magcial use. This and other disadvantages ofnets of the main machine, and its potential the methods commonly in useI have overis likewise raised. Another method has been come by means ofthe present invention, in to commute a part of the main current andwhich I employ two exciting-machines. One pass it around thefield-magnets of the maof these machines furnishes to the field-mag- 8o0 chine itself. This latter arrangement necesnets of the main machineall of the current sitates a somewhat large commutator and the whichthey receive. The armature of this commutation of a considerable portionof the machine has no connection with its own fieldmain current,whilethe single-exciter method magnets, but they are separately excited by ofcompoundinghas several objections,among a second eXciter-machine. It isin a sense a 35 others being the fact that the increase ordecompound-wound machine, in that the windcrease of field strength inthe exciter brought in g upon its field-magnets, which derives curaboutby the commuted main current acts rent from the second eXciter-machine,is a to increase or decrease the current through winding of highresistance, like an ordinary the shunt-winding of the exciter-machine,shunt-winding, and will be hereinafter re- 0 0 and thus produces a sortof geometric proferred to as the shunt-winding. It regression in thechange of potential. This is sembles that class of winding in that acommorc objectionable from the fact that the paratively constant currentis maintained current in the shunt-field winding does not through it.Upon the same field-magnets is respond quickly to the change ofelectromowound a compounding-coil, which derives its 9 5 5 tive force atthe terminals of the winding, energy from the main circuit. In somecases but requires a certain length of time to reach I prefer to mount atransformer upon the its corresponding value on account ofself-inarmature of the main machine and send curduction and resistance,which, added to the rent from the secondary of this transformer lag fromhysteresis, prevents the electromothrough a synchronous commutatormounted 5c tive force in the main machine being quickly upon the shaftof the main machine; but for adjusted to the varying current demand sothis I may substitute other arrangements, in

that case particularly where a stationary transformer is used. By thisarrangement I provide a method of compounding free from thedisadvantages and objections which I have pointed out. The main excitercannot fall below the critical point in its field exciration, becausethe auxiliary exciter furnishes to the shunt-winding a currentsufficient at all times to maintain it above this point. This currentbeing independent of that flowing in the armature of the main exciter,it responds freely to changes in the load upon the main. dynamo, as thecompounding-coil may be of relatively-greater effect with the kind ofexcitation to which I have just referred. The current in theshunt-winding of the main exciter being independent of its own armature,the changes in the field strength produced by the compounding-coil donot directly affect the shunt-coil, and therefore the sluggishness orlack of coincidence between the demand for current and the increase ofpotential due to the compounding-coil does not occur, and theproportionate amount of compounding is not disturbed by this reactiveinfluence of the shunt-coil. It is of course designed to adjust theamounts of the shuntwinding and the compounding-coil to the particulardegree of overcompounding desired.

The method of operation, as will be seen from the above statement ofinvention, is, briefly, to supply the main dynamo fieldmagnetswithcurrent from an armature rotating in a field of force produced by aconstant magnetizing-current independent of the armature itself, and asecond magnetizing force derived either directly or inductively from themain machine, by which is meant either the dynamo itself or the circuitsupplied by it. In speaking of this independent field of force it is,ofcourse understood that the armature reaction is not referred to, butthat there is no electrical connection between the main eXciter-armatureand its own fieldmagnets.

The accompanying drawings show diagrammatic embodiments of my invention,Figure 1 being a representation of the combination of machines that Ihave described with a transformer carried upon the armature of the maindynamo. Fig. 2 is a modified form in which a stationary armature isemployed and a synchronous commutator is used to furnish thecompounding-coil with direct current derived from the main circuit.

Referring now to the drawings by letter, A is the armature of the maindynamo-electric machine to be regulated. B indicates the fieldmagnets. db are the mains from the armature, provided with a pair ofcollecting-rings. A single-phase alternator is indicated; but nothing inmy invention would exclude its application to alternating-machines ofother numbers of phases.

0 is the transformer to which I have referred, mounted upon the armatureof the main machine and connected with its armature-winding at G O. Fromthe secondary of this transformer leads pass to the commutator 0 mountedupon the shaft of the main machine and provided with the usual brushes.From these brushes leads pass to the compounding-coil EF and betweenthese leads a resistance R is shown, which may or may not be adjustable,but ordinarily is of fixed amount. The shunt-coil of the main exciter isindicated at FF, and within the field-coils furnished by these two coilsrotates the armature of the main exciter EA in circuit with thefield-magnets B of the main machine. The shunt-coil is furnished withcurrent from the armature EA of the second or auxiliary exciter, whosefield-magnet FF is in series with its own armature. Aregulating-resistance R for determining the voltage of the main machineand incidentally that of the exciters is interpolated in the circuit atany suitable point.

In Fig. 2 the same reference-letters indicate like parts; but thetransformer C is in the main circuit and is stationary. It suppliesenergy to the armature MA of the synchronous motor M, acting as a rotaryeonverter, the field-magnets of which are supplied with current from theauxiliary exeiter. The portion of the main current transmitted byinduction through the transformer O is fed to the armature of thisconverter and is there rectified by the commutator and fed to thecompoundingcoil EF The electrical operation of the devices justdescribed will be readily apparent to those skilled in the art, whilethe advantages of the method of operation have been pointed out above.

It is manifest that another source of current for supplying the constantexcitation of the main exciter might be substituted for the auxiliarydynamo which I have shown. Such a source of current is indicated in Fig.1 in dotted lines, a storage -battery being diagrammatically shown at Swith a resistance R in its circuit for adjusting the electromotiveforce, although any other means might of course be used.

In addition to the advantages which I have already stated I am enabledby the combination of apparatus and method of operation which I haveillustrated and described to dispense with potential-responsive magnetsas employed in many forms of regulator now in use, and I also dispensewith contacts to be opened and closed by the action of suchpotential-responsive devices, thus overcoming the objections not only tothese devices but to the auxiliary arrangements so often necessary toeliminate the sparking in their operation.

WVhat I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. The method of compounding alternatingcurrent dynamo-electric machinesfor change of potential under change of load, which consists insupplying to the field-magnets cur= rent from an armature revolving in acompound field of force independent of the armature itself, part of suchfield of force supplied by a separate excitation substantially fixed inamount, and part by a commuted current derived from the main machine.

2. The method of compounding alternatin gcurrent dynamo-electricmachines for change of potential under change of load, which consists insupplying to the field-magnets current from an armature revolving in acompound field of force independent of the armature itself, part of suchfield of force supplied by separate excitation substantially fixed inamount and part by a commuted current derived inductively from the mainmachine.

In combination, an alternating-current dynamo-electric machine, anexciter-armature in circuit with its field-magnet winding, a coil ofhigh resistance upon the field-magnets of the exciter, an externalsource of current for the coil, and another coil upon the field-magnets,the latter coil deriving its energy from the alternator.

4:. In combination, an alternating-current dynamo-electric machine, anexciter-armature in circuit with its field-magnet winding, the latterarmature having no electrical connection with its own field-magnetwinding, a coil upon the exciter field-magnets in circuit with a sourceof substantially constant electromotive force, and a compounding-coilupon the exciter field-magnets deriving energy by induction from themain circuit.

5. In combination, an alternating-current dynamo-electric machine, anexciter-armature in circuit with its field-magnet winding, an auxiliaryexciter supplying a field-magnet coil upon the main exciter withsubstantially constant electromotive force, a compounding coil upon thefield-magnets of the main exciter, and a synchronous commutatorrectifying part of the main current and supplying it to thecompounding-coil.

(3. In combination, an alternating-current dynamo-electric machine, amain exciter-armature in circuit with its field-magnet winding, anauxiliary exciter, a synchronous converter, a high-resistance coil uponthe fieldmagnets of the main exciter, electrical con nections from theauxiliary exciter to the high-resistance coil and the field-magnets ofthe converter, and a compounding-coil upon the field-magnets of the mainexciter and in circuit with the converter.

In witness whereof I have hereunto set my hand this 14th day of January,1896.

WALTER S. MOODY. lVitnesses:

JOHN XV. GrBBoNEY, HENRY M. HOBART.

